For patients already taking thyroid hormone, there is often an increased required for thyroid hormone during pregnancy, and the dose of the thyroxine tablet may need to be increased several times during the course of the pregnancy to keep thyroid hormone levels in the normal range. This is generally the case for patients who have had all or part of the thyroid removed surgically, or who have had radioactive iodine treatment for hyperthyroidism, but may be seen in all types of hypothyroid states.

Hypothyroidism

Hypothyroidism detected in a woman planning pregnancy, or in a pregnant women should be corrected with thyroxine replacement. As the course of pregnancy evolves and the pregnant woman gains weight, the dose of thyroxine may need to be increased to keep the TSH in the normal range. Thyroxine (T4) given to pregnant patients with hypothyroidism does not cross the placenta in significant quantities, is identical in structure to the thyroxine normally made by the thyroid, and is safe to take during pregnancy and during breastfeeding.

Accumulating evidence suggests that it is important to maintain normal thyroid function in the mother for optimal development of the baby.

In the Aug 1999 issue of the New England Journal of Medicine, a study reported results of neuropsychological testing (IQ tests, school performance, language and reading skills, visual and motor performance) in 62 women with varying degrees of hypothyroidism during pregnancy. There was a small but significant difference in IQ scores in children whose mothers were not treated for their hypothyroidism during pregnancy. These results reaffirmed the importance of maintaining thyroid function at a normal level in woman planning a pregnancy, and in pregnant women. As thyroid hormone requirements commonly increase during pregnancy, pregnant women taking thyroid hormone should be appropriately monitored to make sure their TSH remains in the normal range.

A non-randomized retrospective study of maternal hypothyroidism and IQ testing in 8 year old children of previously hypothyroid mothers found an inverse relationship between the levels of TSH during pregnancy and subsequent IQ levels in children of mothers with significant hypothyroidism during pregnancy. Although this type of study lacks important controls and attributes one would like to see in a prospective study, it adds more evidence in support of maintaining normal levels of thyroid hormones in pregnant mothers. See Relation of severity of maternal hypothyroidism to cognitive development of offspring. J Med Screen. 2001;8(1):18-20.

Lazarus and colleagues carried out a randomized trial in which thyroid hormone levels were obtained from pregnant women (21,846 study participants) at or before 16 weeks gestation (mean gestational age at which blood work was done was 12 weeks, 3 days), and the women were randomized to possible intervention (thyroid hormone replacement) based on actual results of thyroid hormone tests obtained immediately at the time of testing (Group A), or simply follow up with no review of blood work and no intervention (Group B). Women in Group A with evidence for hypothyroidism were treated with 0.15 mg levothyroxine (T4) daily. The primary outcome in this study was IQ test results in babies born to all women, assessed at 3 years of age, by psychologists who had no knowledge of maternal treatment or disposition. In women with detected hypothroidism (very low T4, elevated TSH, or both) who required treatment (390)in the intervention group, their children exhibited comparable results in subsequent tests of intelligence and cognitive function compared to the children of mothers (404) in the control group who had similar levels of thyroid dysfunction but received no intervention. Hence, antenatal screening of women to detect hypothroidism, did not appear to produce a benefit as evaluated in children at 3 years of age. Whether benefit may have been detected if treatment was started earlier or children were tested at older ages remains unknown. Antenatal thyroid screening and childhood cognitive function N Engl J Med. 2012 Feb 9;366(6):493-501

Accordingly, patients with a history of hypothyroidism, especially those taking thyroxine, should have their TSH monitored prior to and several times during pregnancy, perhaps every 8-12 weeks, or more frequently depending on the pattern of weight gain, to ensure that the TSH and levels of free thyroid hormones remain in the normal range throughout pregnancy.Some patients with a history of thyroiditis may require a bit more
thyroid hormone in the postpartum period Increased
Postpartum Thyroxine Replacement in Hashimoto's Thyroiditis Thyroid.
2010 Jul 8. [Epub ahead of print]. Whether all women should have thyroid hormone testing early in pregnancy remains uncertain.

Hyperthyroidism

Pregnant patients with hyperthyroidism should not have a radioactive iodine uptake or thyroid scan, and may require treatment with antithyroid drugs such as propylthiouracil (PTU) or methimazole. In some centers, if Graves disease is suspected, a thyroid stimulating immunoglobulin (TSI or LATS) test (a simple blood test) is obtained to determine if the expectant mother has circulating antibodies that may cross the placenta and stimulate the baby's thyroid. These antibody tests are not absolutely required for management of pregnant women with Grave's disease, and are usually only available in research centers.

Although methimazole is not absolutely contraindicated during pregnancy, PTU is the preferred antithyroid drug for the pregnant women.

Nausea, vomiting and hyperemesis gravidarum

Some women develop intractable nausea and vomiting often in the first trimester, leading to weight loss and dehydration and treatment may require hospitalization. A subset of pregnant women with nausea and vomiting may be found to have mild abnormalities in thyroid function, often a slight elevation in T4 and/or suppressed TSH. In the majority of women, supportive treatment without the use of antithyroid drug therapy results in the resolution of the nausea and vomiting and thyroid function frequently returns to normal without treatment. Some women may develop mild hyperthyroidism due to increased HCG production or increased sensitivity to HCG, a placental hormone that has weak TSH-like activity. Hyperthyroidism that presents only with nausea and vomiting often resolves by the second trimester, and is not associated with adverse outcomes. See Transient hyperthyroidism of hyperemesis gravidarum. BJOG. 2002 Jun;109(6):683-8.

Postpartum Thyroiditis

Thyroid dysfunction may develop after childbirth, and may include hyperthyroidism, hypothyroidism, or both. For more information, see Postpartum Thyroiditis.

Thyroid cancer

Pregnant women with thyroid cancer should also have their TSH monitored a few times during pregnancy, as weight gain and metabolic changes of pregnancy may result in an increased requirement for thyroid hormone to keep the TSH at an appropriately suppressed level. If surgery is required during pregnancy, many specialists advocate waiting till the second trimester to try and minimize effects on the baby. Given the slow growing nature of many thyroid nodules and thyroid cancers, the physician and patient should discuss the individual pros and cons of thyroid surgery during pregnancy on an individualized case by case basis.

FAQs

I did not know that I was pregnant and inadvertently had a thyroid scan with a radioactive isotope at 7 weeks gestation. What will happen to my baby?

Specialized unique circumstances such as these should be discussed with an endocrinologist and obstetrician. The human fetal thyroid develops between 10-12 weeks of age, hence inadvertent administration of radioactive iodine isotopes to pregnant women earlier than 8 weeks of age will not usually affect fetal thyroid development. There is very little good clinical data from studies of this problem other than occasional case reports, hence management needs to be done on an individualized basis.

I just found out I have thyroid cancer and I am pregnant-when
should I have my surgery?

I want to have a baby in a few years time. Should I avoid radioactive iodine treatment for my Graves' disease?

Although some physicians and patients prefer to avoid radioactive iodine in young women of childbearing age, there is little scientific evidence to suggest that radioactive iodine must be avoided in such patients. The optimal treatment of such individuals depends on many factors, and specific treatment options should be discussed by each patient with her endocrinologist. Some thyroid specialists might argue that it is better to definitely treat hyperthyroidism prior to planning a pregnancy with radioactive iodine or surgery, so as to avoid the risk of relapse or the need for antithyroid medication during pregnancy.

My TSH has been borderline elevated but I feel fine, and I am trying to get pregnant. Do I need to take thyroid hormone?

Although subclinical hypothyroidism (patient feels fine but the blood tests shows mild hypothyroidism) does not invariably need to be treated in many patients, women planning a pregnancy should maintain normal levels of thyroid function both before during and after pregnancy. The risk of miscarriage appears slightly raised in hypothyroid women, and hypothyroidism may affect ovulation and ability to become pregnant, as well as placental abruption and preterm birth. See Subclinical hypothyroidism and pregnancy outcomes. Obstet Gynecol. 2005 Feb;105(2):239-45.

My TSH has been found to be low during pregnancy, but
I feel fine-do I need treatment?

The answer to this question clearly depends on the
individual patient and clinical circumstances. However, for pregnant
patients with "subclinical hyperthyroidism", namely a low TSH
but otherwise normal levels of thyroid hormones, there does not appear
to be any significant adverse outcome, and treatment of the abnormal TSH
level may not be required as described in Subclinical
hyperthyroidism and pregnancy outcomes.Obstet Gynecol. 2006
Feb;107(2):337-41

I have just had a miscarriage and my thyroid tests are abnormal. Is there a connection?

Both thyroid disease and miscarriages are common, and many women may experience both at some point. Uncontrolled hyper or hypothyroidism may be associated with a slightly increased risk of miscarriage. Furthermore, some, but not all studies show an increased prevalence of thyroid antibodies in women with recurrent miscarriage. Overall, it seems prudent to ensure that thyroid status is as normal as possible is women contemplating pregnancy.

I am pregnant, my TSH is suppressed and my doctor says I am hyperthyroid. Do I need treatment?

The detection of a suppressed TSH with normal levels of Free T4 and Free T3 is not uncommon. Furthermore, the symptoms of pregnancy and hyperthyroidism are both non-specific and overlapping (fatigue, warmth, occasional increases in heart rate, trouble sleeping etc). In some cases, it is appropriate to monitor the blood tests and clinical status without invariably instituting antithyroid drug therapy. In other instances, if the physician is concerned that the patient is actually hyperthyroid, a low dose of an antithyroid drug may be instituted. Patients need to be evaluated carefully by their physician and a discussion of the pros and cons of the various management options is required for each individual patient.

I am pregnant and have thyroid disease. Will my baby also have thyroid problems?

The answer depends on the type of thyroid disease and pattern of genetic inheritance. Patients with autoimmune thyroid disease such as Graves' disease or Hashimotos thyroiditis will usually pass on a higher risk of developing these diseases to their children. Some patients also have a strong family history of enlarged thyroid glands or multinodular goiters that may also be passed on in subsequent generations. In contrast, most forms of thyroid cancer do not have a genetic basis. As the majority of thyroid disease are treatable with good outcomes, this should not be a major source of anxiety for most pregnant mothers.

I have thyroid disease from amiodarone and I am pregnant. Will the amiodarone affect my baby?